Indications for the replacement of the radial head can include: a) degenerative or post-traumatic disabilities presenting pain, crepitation, and decreased motion at the radio humeral and/or proximal radioulnar joint with: joint destruction and/or subluxation visible on x-ray; and/or resistance to conservative treatment; b) primary replacement after fracture of the radial head; c) symptomatic sequelae after radial head resection; and d) revision following failed radial head arthroplasty.
In radial head replacement procedures, a radial head prosthesis is implanted into the intramedullary canal of the proximal radius. The radial head may cooperate with an ulna or ulnar prosthesis to provide radioulnar joint articulation. The radial head may cooperate with a humerus or humeral prosthesis to provide radiohumeral joint articulation.
Some radial head implants known in the art include a head portion having a cylindrical shape and/or straight sides. These implants may provide only point contact with an ulnar component. In addition, it can be difficult to implant a radial head prosthesis into the intramedullary canal at a precise angle or relationship to the ulna. If the radial implant is not inserted at a precise angle relative to the ulnar component, surface contact with the ulnar or ulnar prosthesis may not be achieved.
Disclosed herein is a radial head implant including a head and a stem. In an embodiment, the head portion is symmetric and non-cylindrical, and has sides formed of multiple arc segments, with no straight sections. This shape provides surface contact between the radial head and an ulna or ulnar component. This shape also accommodates a radius whose proximal canal axis is not parallel with the articulation surface of an ulnar component. A concave portion is provided near a distal end of the head, which may provide easier insertion into the joint space by permitting a smaller angle of approach to the radial medullary canal when passing near the distal humerus. In an embodiment, the stem is straight and has a bullet-shaped tip, which may provide easier insertion into the intramedullary canal than would other shapes including a squared-off end.